1. Field of the Invention
The invention relates to the field of plumb and leveling equipment, and in particular concerns a device for use in conveniently obtaining or checking multiple parallel lines on an inclined plane, for example, in connection with the installation of roofing materials.
2. Prior Art
In the building trades, it is often useful to obtain multiple reference lines which are used to align successive rows or courses of building materials. A builder may mark a series of parallel lines on a vertical exterior wall of a building prior to applying siding such as clapboards or shingles and the like. When applying siding to a vertical wall surface, it is preferable to employ reference lines that are horizontal (i.e., in a plane parallel to the horizon), parallel and evenly spaced. A first reference point is marked on the wall surface and a spirit level or the like, typically having a bubble in a curved fluid-filled tube, is used to draw a horizontal line from the point to provide an initial reference line, for example by snapping a chalked line. The vertical position of the initial reference point is selected to locate the first row of siding or the like, typically called the starter course, accurately with respect to the horizontal edge of the structure, and for appearance purposes precisely horizontal.
For providing successive reference lines for the respective courses, a vertical measurement can be taken from two spaced points along the initial reference line, at a distance sufficient to provide the proper amount of exposure vs. overlap of the courses. These spaced points (which may be endpoints) are connected by snapping a chalked line and/or the line is otherwise extended horizontally. Horizontal lines can be readily drawn on a vertical surface using a carpenter's level. Using a level is more accurate than relying only on measurements from spaced points on a previous line, because measurements can introduce errors that are carried along into the successive courses and can be cumulative. To maintain horizontal courses as the work proceeds from the starter course, it is useful to check that the reference lines remain horizontal, at least for some of the successive reference lines.
This procedure can become more complicated in cases where the underlying base for the successive rows, or the edge of the structure, is other than vertical. In the roofing trade, the problem is compounded by the pitch of the roof, the possibility that the eaves or roof ridge may not be horizontal, the possibility of a gradient that is not in a vertical plane, the potential inclusion of additional configurations such as gables, dormers and the like, and the fact that the roof surface may have bumps and irregularities. It is desirable to obtain multiple parallel reference lines on an inclined roof surface, notwithstanding such difficulties, when installing shingles or other materials to the roof surface. This is necessary to maintain planned alignments of the courses with the eaves, the ridge of the roof, and with potential gradient change lines, for example, in gambrel roof configurations.
Several techniques can be used in an effort to obtain a series of parallel lines on an inclined surface such as a roof. For example, parallel lines can be established from a base line by using a tape measure to measure a fixed distance from the base line to a point. The measurement is repeated identically on each end of the roof. A chalk line is stretched between the two points and is used to snap a line which is parallel to the reference line. This process can be repeated multiple times to establish a series of parallel lines used for reference in applying courses of roof shingles and the like, but it relies on the structure being accurate, and any error introduced on a given course is carried along to successive courses.
U.S. Pat. No. 1,305,062--Vroome discloses a line holder which can be operated by a single person in order to snap three successive parallel chalk lines a predetermined distance apart. The line holder has a spring loaded pivoting arm which is operable to hold one end of a chalk line and is movable between three distinct positions where the line is successively struck. The line holder is useful for determining a reference line position on only one side of the roof. The operator must place the opposite end of the chalk line at the proper position when the line is struck, and thus must match the distance between the arm and a reference point on the first side, to avoid introducing an error.
For vertical surfaces, a spirit level is useful to double check lines at the later courses. However, strictly horizontal reference lines are not always the object, especially for an inclined surface such as a roof. Parallel lines at other angles may be desirable, for example, to match a non-horizontal edge along eaves or to mark an edge approaching a hip for installation of flashing, or for other purposes. These reference lines are difficult to obtain except by careful measurement from an initial reference line.
It would be desirable to verify the accuracy of parallel reference lines on a roof or the like, including lines other than horizontal ones, using a device that is as useful as a spirit level on a vertical wall. However, known spirit levels and mechanical gravity responsive levels are not useful on inclines, particularly if the gradient is partly diagonal, because it is not possible to distinguish between an indication that is due to variation of the level from the desired line in a plane parallel to that of the incline, and one due to variation of the level perpendicular to the plane of the incline. Most spirit levels and mechanical gravity responsive levels therefore are specifically designed to indicate a specific standard incline only, such as 0.degree., 45.degree. or 90.degree., and are not helpful for matching any line on an inclined surface of an arbitrary pitch.
In connection with levelling apparatus, it is known to provide a form of level for determining horizontal alignment. An example is a level for a phonographic turntable. Such levels have a flat base for resting on the turntable or other surface and a quantity of liquid in a transparent domed receptacle with a circle or crosshair marking at the top center of the dome. A bubble in the liquid is aligned to the circle or crosshair marking when the surface is level, and is diverted in any direction around 360.degree. when the surface is not level. Such levels have no point of reference other than the top center of the dome, where the bubble and circle or crosshair marking show the gradient direction.
Two levels arranged on perpendicular axes can be used to define the slope of an arbitrary line on an incline. U.S. Pat. No. 1,258,597--Mladinich, for example, discloses such a device with two pendulums on perpendicular pivot axes, a transverse axis pendulum being gimballed to a longitudinal axis pendulum. The pendulums indicate tilt on an axis parallel to a line of elongation of the tool, and on an axis transverse to the line of elongation, but the axes are spaced above the base of the device, and thus spaced above the surface of the incline. It would be possible to place the Mladinich device at a given point on the inclined plane and at a given alignment; to note the two angular readings; to move the device to a new location a distance away (preferably a measured distance); and, to adjust the device there to obtain the same two angles. Theoretically, this would produce parallel lines. However, it is unwieldy due to the two indicators. The readings of both indicators change simultaneously when moving the device in any direction other than rotating it around one of the axes. Whereas the axes are spaced above the base, the readings can be changed by lifting one end of the device.
In addition to the disadvantage that the operator is required to make two separate readings while hunting for the desired orientation of the device, another aspect is that the device has a flat base surface parallel to one of the axes, which must be rested on the surface to be measured. A roof surface may have variations in inclination, as well as imperfections such as cups, warps, high spots, low spots or other dimensional variations. Such variations affect the reading obtained from the tilt measuring device.
It would be desirable to provide a tool that can be used to obtain multiple parallel lines on an inclined surface without relying on a flat base that must rest against the roof surface, which has a single indicator, and which is read as conveniently as a spirit level.